I bought a 200 on 185 off fan switch and I put it in the passenger side cylinder head and it isn't working. I know if I ground the wire going to it , then the fan comes on. So does this mean the switch is bad?
thanks

 

We know your fan is working. Soooo, the questions are:

1. Did you put teflon tape on the switch threads
2. How did you determine "not working"?

 

I thought that if I used teflon tape it would mess up a ground, so I only put it on a little bit of the threads. I will try and take it all of though and try it again. I don't think it's working because the fan comes on at the same temp still.

 

When the temp goes up the resistance goes down. When it reaches a certain figure and enough current goes thru the sensor the fan relay clicks on and turns on the fan. That is about how it works in a nutshell, I believe. By you puting teflon tape on the sender's threads, you might alter the resistance so I would clean them off altogether.

Next, keep the car in idle and see when it comes on and get an infra red thermal scanner on the sender and see what temp it is. Your gague could be far out.